Method of grinding and grinding wheel therefor



March 3, 1959 I c, GARRlSQN 2,875 559 METHOD OF GRINDING AND GRINDING WHEEL THEREFOR Filed Oct. 30, 1956 I 2 Sheets-Sheet 1 INVENTUR CZ [if [71217 I. 622221317121 3, 1959 r L, n so 2,875,559

znmmon 0F GRINDING AND GRINDINQ THEREFOR 2 Sheets-Sheet 2 Filed not. so, 1956 ad" 'JNVENTUH:

CL JFPUM z. FARE/.5 01y".

United StatesPatent O F GRINDING AND GRINDING WHEEL THEREFOR I METHOD This invention relates to a grinding wheel and a method of forming, grinding, or sharpening metal objects or tools and more particularly to a method of configurating and sharpening form tools or form tool bits fashioned of comparatively hard materials and to a novel grinding wheel construction.

In the manufacture of cutting tools such as form tool bits of the character employed in machining operations for cutting metals and metal alloys, form tool bits have been made and utilized which are fashioned from materials which are extremely hard. One such material or alloy utilized for tools or tool bits is tungsten carbide.

Form tools or cutting tools made of tungsten carbide or similar hard materials must be ground or abraded to the proper shape or configuration for use in cutting operations, and by reason of the extreme hardness of the material, grinding methods heretofore used for shaping a tool to the proper configuration or resharpening a dull tool have notbeen very satisfactory or elficient.

When a tool bit formed of tungsten carbide or the like is brought into contact with a conventional grinding wheel having an uninterrupted circular grinding surface, the tool is not readily abraded or ground by the wheel and there is a tendency for the tool to be burned because of the high friction heat developed. Furthermore the cutting edge does not always become smooth and sharp but may be chipped or broken due to brittle characteristics of the hard material and the grinding wheel surface glazed by the contact of the hard material.

Applicants Patent 2,607,173 granted August 19, 1952, discloses method involving the use. of a grinding wheel having transversely arranged slots or interrupted zones at the periphery of the wheel to effect successive impacts of the spaced zones of the wheel against the region of the tool being shaped or sharpened whereby the tool is vibrated in directions toward and away from the wheel and the material of the tool removed by the successive impacts without burning the tool or glazing the wheel surface. The grinding wheel disclosed in applicants patent for carrying out the patented method is provided with peripheral slots, the bounding walls of the slots being in planes parallel to the axis of rotation of the grinding wheel.

Applicant has found that in grinding form tools according to the invention forming the subject matter of applicants patent where the upper surface of the form tool is disposed in a substantially horizontal position with respect to the grinding wheel rotating about a horizontal axis, the tool engaging edges or regions of the grinding Wheel engage or contact the horizontally disposed tool surface throughout substantially the width of the tool surface in a substantial linear area.

The edge of the tool may not be sharpened to the desired degree of sharpness because of the cutting edges of the segments of the grinding wheel engaging the tool in a substantial linear area which may extend full width 2,875,559 Patented Mar. 3, 1959 ICC stantially a point contact so that successive impacts of spaced regions of the grinding wheel with the tool provides efiicient grinding in a comparatively short time and a smooth cutting edge imparted to the tool.

Another object of the invention is the provision of a grinding method wherein spaced rectilinear regions of a grinding wheel disposed diagonally relative to the axis of the grinding wheel are successively engaged with a tool or other element to be ground or abraded so as to efiect .a progressive shearing action in abrading or cutting the ,tool whereby the grinding is effected at an increased rate without breaking or chipping the material of the tool at the zone of engagement of the wheel with the tool. Another object of the invention resides in a method of I grinding cutting tools or other hard metal objects Wherein successive regions engaging the tool or other object are formed in alternately directed angular or diagonal positions in the grinding wheel periphery whereby successive impacts of the regions of the wheel adjacent the grinding or cutting region eifect progressive shearing actions on the tool or object in alternately opposed directions whereby more uniform cutting or abrading of the tool is attained.

Another object of the invention involves a method of abrading tools formed of hard materials by engaging the tool with an instrumentality configurated to impinge upon the material in a manner imparting successive blows or impacts to the material effective in alternate opposed directions to set up vibration of the tool whereby increased efficiency of abrasion is attained.

Still another object of the invention resides in a method of engaging a body with a grinding instrumentality configurated to present body engaging regions extending in divergent directions which are arranged to engage the body in rapid successive impacts whereby the body is caused to vibrate or oscillate in longitudinal and transverse directions whereby grinding efliciency is greatly increased.

Another object of the invention resides in a method of grinding utilizing a grinding medium having an interrupted grinding area arrangement for cooperation with a cutting tool and support whereby the extent of movement of the cutting tool into engagement with the grinding medium is predetermined or restricted.

Another object of the invention is the provision of a grinding wheel configurated with spaced recesses or slots arranged in the peripheral zone of the wheel and extending in diagonal directions with successive recesses extending in alternate diagonally opposite directions.

Another object of the invention resides in a grinding wheel having a peripheral region configurated with slots disposed in askew positions with successive slots extending in divergent direction.

Further objects and advantages are within the scope of this invention such as relate to the arrangement, operation and function of the related elements of the structure, to various details of construction and to combinations of parts, elements per se, and to economies of manufacture and numerous other features as will be apparent from a consideration of the specification and drawing of a form of the invention, which may be preferred, in which:

Figure 1 is a front elevational view showing a-. form of the method of the invention.

Figure 2 is a side elevational view showing a portion of the apparatus illustrated in Figure 1.

Figure 3 is a side elevational view of a grinding or abrasive wheel embodying a form of the invention;

Figure 4 is a front elevational view of the grinding region of the wheel shown in Figure 3;

Figure 5 is an isometric view of the grinding wheel shown in Figures 3 and 4;

Figure 6 is an elevational view illustrating a modified form of grinding wheel of the invention, and

Figure 7 is an isometric view of the wheel configuration illustrative in Figure 6.

While I have illustrated anapparatus especially adapted to carry out the method of the invention utilizing novel forms of grinding or abrasive wheels for grinding or shaping form tool bits, it is to be understood that the principles of the invention may be utilized in forming, grinding or abrading other objects or articles.

Referring to the drawings in detail and particularly to Figures 1 and 2 thereof, the grinding apparatus illustrated is inclusive of a base 10 which supports an upwardly extending frame 11. The base member supports a receptacle or trough 12 defined by a peripheral flange 14 which is adapted to receive cooling fluid that may be utilized to cool the grinding wheel and the object or tool being ground.

The base 10 encloses a fluid pump (not shown) which circulates fluid from a reservoir contained in the base through a flexible pipe 15 to a manifold 16 from which the fluid is directed onto the grinding region of a grinding or abrasive wheel 18. The grinding wheel 18 is fixedly mounted upon a shaft 20 which is journaled in suitable bearings in the frame structure 11. The shaft 20 is equipped with a pulley 21 driven by a belt 22 from a motor (not shown), the belt and pulley, arrangement being enclosed within a casing or cover 24.

The grinding wheel 18 is substantially enclosed within a housing or casing 26 and the member 38 is formed with a work access opening 28, the casing 26 being mounted upon a shaft 27 and arranged for adjustment about the axis of the shaft 27; The housing 26 of the machine is provided with a boss 29 which is bored to receive a shaft 30 which is equipped with a hand wheel 31 at one end, the opposite end region being threaded into a nut or bushing 32 which is pivotally supported upon a projection 33 formed on the frame 11. Rotation of the hand wheel 31 and shaft 30 effects a pivotal movement or adjustment of the housing 26 about the axis of the shaft 27.

The frontal portion of the housing 26 is formed with vertically disposed ways or tracks 36 of dove-tailed cross section which slidably support a member 38. The upper portion of the housing 26' is formed with a boss 40 which is bored to snugly receive a bushing 41. The bushing 41 is interiorly threaded to receive the threaded portion 2,875,569 r if 43 of a shaft 44. A plate 45 secured to the upper end of the slidable member'38 is bored to receive the unthreaded portion of the shaft 44 as shown in Figure 2.

Secured to the upper end region of the shaft 44 is a manipulating or hand wheel 46. Rotation of the hand wheel 46 raises or lowers the slide member 38 dependent upon the direction of rotation of the'hand wheel. In the operation of configurating or sharpening form tools or form tool bits of tungsten carbide or the like, a suitable tool holder 67 is equipped with a templet 74 of the configuration desired to be formed on the tool or tool bit.

The apparatus illustrated is inclusive of a templet shaping or grinding wheel 50 mounted upon a shaft51 and driven by an electrically energized motor 52. The grinding wheel 50 is enclosed within a suitable casing or housing 54 having an opening 55 to facilitate engagement of the templet 74 with the grindingwheel.

The motor 52 for driving the template shaping wheel is mounted upon a plate 57' adjustable in a direction axially of the motor 52 through the medium of a threaded shaft 58 equipped with a hand wheel 59. The threaded shaft 58 is threaded into a sleeve inserted in a bore formed in a member 60 secured to the frame portion 11 of the apparatus.

A tool holder support or supporting means in the form of a semi-spherically shaped member 64 is secured to a ledge 65 formed on the frame of the machine. The member 64 is adapted to provide a universal support for a combined tool holder and templet carrying means 67, which in Figure 2, is illustrated in tool grinding position.

Secured to the machine frame 11 is a gauge or abutment block 69 which, in forming a templet, is adapted to be engaged by a master form tool or bit of a predetermined configuration or shape which is to be imparted to the templet. The tool holder 67 is provided with a block or member 71 formed with a groove or recess of a dimension to receive and accommodate a form tool bit 72. The block 71 and the tool bit 72 are adapted to be clamped to the tool holder 67 by suitable cam means (not shown).

The upper end of the tool holder 67 is arranged to support a templet 74 held in place by means of a clamping member or screw 75. When the holder 67 is adapted to be utilized to shape or configurate a templet 74 to the shape of a master form tool for subsequent grinding or shaping of other tool bits or blanks, the templetform: ing operation is carried out in the following manner:

The master form tool is clamped to the tool holder in the supporting block 71 so as to securely lock the master form tool in the tool holder 67. The lower end of the tool holder 67 is formed with a semi-spherically shaped recess or socket 77 which is adapted to snugly fit over the ball-shaped support 64 carried by. the ledge 65. The templet or template blank is secured to the upper end of the holder 67 by means of the clamping screw 75. The templet is adjusted so that the shaped or configurated end of the master form tool is close to but not in engagement with the abutment block 69, in

- which position the templet will engage the grinding wheel 50 so as to be shaped or ground to the proper configuration.

With the holder 67 mounted upon the ball 64, the operator exerts pressure upon the holder 67 toward the grinding wheel 50 to bring the forward edge zone of the templet into contact with the wheel. The grinding continues until all portions of the master form tool carried by the holder contact or engage the abutment block 69. When this condition obtains the shaping or profiling of the templet 64 is completed, the abutment block 69 cooperating with the master form tool as a limiting means for determining the extent of grinding of the templet 74.

The apparatus is also provided with a gauging means for coordinating a form tool blank carried by the holder 67 in proper relation to the templet to limit or restrict the amount of metal to be ground or removed from the form tool blank at one grinding operation. As shown in Figure l, the machine frame 11 is provided with an other ball-shaped support 80 adapted to be received in the recess 77 formed in the end of the tool holder 67.

Positioned above the support 80 is a gauge plate 81 adapted to be engaged by a form tool blank carried by the holder 67.

Also supported upon the machine frame 11 is an upwardly extending member 83 which has a threaded bore adapted to receive a threaded tenon formed on a rotatable gauge block 85. The gauge block 85, being threadedly supported in a bore in the member 83, provides an arrangement forming a micrometer adjustment for the gauge block 85 whereby the block may be adjusted to a particular position for predetermining the amount of metal to be rernoved a grinding operation.

from the form toolblank during 'Inthe use of the gauge, the gauge block is adjusted to proper position and the templet 74 is engaged with the face of the block. The form tool blank carried by the holder 67 is then adjusted in the supporting block or holder 71 with the end of the blank to be ground in contact with the positioning or gauge block 81 and the form tool blank locked in the tool holder 67.

In this manner the form tool blank is preadjusted so that when the tool bit orblank is subsequently brought into engagement with the tool grinding wheel 18, only wheel.

The slidable member 38 is formed with a ledge 90 as shown in Figure 2 upon which is mounted a ball-shaped toolholder support 92 which, as shown in Figure 1, is arranged in a vertical plane passing through the centralregion of the grinding wheel or unit 18 and normal to the axis thereof. The upper portion of the member 38 is provided with a straight edge 94 which functions as a gauging or movement-limiting means for the tool holder in a direction toward the grinding wheel by reason of engagement of the templet 7'4 with the straight edge 94.

In performing grinding operations upon a form tool blank or other metal objects 72, after the position of the blank has been determined through the utilization of the gauge blocks or members 81 and 85 hereinbefore described, the tool holder 67 is placed upon the ball-shaped support 92 carried by member 38 and the operator exerts yielding pressure uponthe .tool holder in a direction toward the grinding wheel. As the form tool blank 72 engages the grinding wheel'prior to engagement of the templet 74 with the straight edge 94, grinding of the operative end of the form tool blank or object 72 will ensue until all portions of the forward edge of the term plet 74 engage and contact the straight edge 94.

g It should be noted that through the use of a spherically -shaped support 92 for theholder engaging in a semispherically shaped recess 77 in the holder, the latter may be rota'ted through sufficient angles and oscillated about the center of the ball 92 so that any straight or convex form may be imparted to the blank 72 in accordance with the pattern provided by the shape of the templet 74. The slidable member 38 is adaptedto be adjusted in a vertical directionrelative to the grinding wheel or unit 18 by manipulation of the hand wheel 46 to engage the form tool blank 72 at a zone above a horizontal plane through the axis of the grinding wheel in order to form a proper clearance or relief angle beneath and adjacent the cutting edge.

The present invention embraces an improved method of grinding form tool bits .or other metal, bodies and includes novel forms of grinding Wheel or unit especially usable in grinding or configurating tools or bodies formed from tungsten carbide or other very hard metal alloys Without burning the tool or body and without chipping of the tool engaging regions of the grinding Wheel. p

In my prior Patent No. 2,607,173, there is illustrated a grinding: wheel configurated. with radial slots bounded by walls which liein planes parallel to the axis of rotation of the grinding wheel. In most shapes of form tool hits, the upper 'surface of the bit is substantially horizontal or is fashioned with a slight rake angle, the degree thereresults in chippingor flaking of theleading edges of the grinding zones which is apparently due to the impact of the transversely extending tool engaging region of a peripheral section of a grinding wheel throughout a line contact with the frontal edge or nose of the form tool.

The method of grinding disclosed herein and the novel forms of grinding wheel for carrying out the method effectively, prevent or greatly minimize the tendency of the leading edges of peripheral sections or segments of the grinding wheel to become chipped as well as to greatly, increase the speed of effective grinding or abrading of the tool through the provision of a progressive engagement of successive grinding wheel sections or segments with the work being ground.

The method of the invention more specifically provides for a shearing action of a grinding or leading edge of a wheel section with'the tool being ground, and successive shearing actions against the tool may be etfected in alternate, generally opposed directions. Such grinding action sets up a minute, though high-frequency, transverse oscillation or vibration of the region of the tool engaging the grinding wheel which augments or increases the dicetiveness and efficiency of the grinding operation.

One form of grinding wheel for carrying out the method of the invention is illustrated in Figures 1 through 5. In this form the grinding wheel or unit 18 is of a generally cylindrical character having a circular periphery. The peripheral region of the wheel is formed with circumferentially spaced slots or recesses 100, preferably equally spaced, which are angularly arranged with respect to the axis of the grinding wheel, each of the re cesses extending in the same general direction with relation to the axis of the grinding wheel. The recesses 100 may be defined as disposed in an askew, diagonal or oblique relation to the planes of the side walls of the grinding wheel.

In the form of wheel shown in Figures 1 through-5, the slots 100 are defined by parallel walls 102, the width of the slots 100 being greater than the Width of the form tool blank so that the end region of the tool blank may enter slightly into each recess in order to obtain the benefit of the impact of the tool engaging or impinging edges formed at the intersection of a wall 102 with the adjacent peripheral region 106 of a grinding wheel section.

Formed in the periphery of the wheel is another series of slots 110, each slot being substantially equally spaced between each pair of the slots 100. The slots 110 extend in an angular direction generally opposite to the angular direction of the slots 100. Theslots 100 and 110 of each pair are in converging relation and are of equal angularity at each'side of a plane through the zone of convergence and through the axis of the wheel.

Each of the slots 110 is defined by parallel walls 112 and, when the wheel is rotated in the direction indicated by the arrow in Figure 5, the leading edge 114 defined by a side wall 112 of a slot 110 and the adjacent peripheral surface 106 of the grinding wheel forms an impinging region or zone on the periphery of the wheel which extends in an angular direction substantially equal and opposite to the angular direction of the impinging edge 105 of the grinding wheel.

Thus during grinding operations, the tool engaging or impinging regions 105 and 114 of alternately angular slots 100 and 110 progressively engage the form tool being ground or configurated in a transverse shearing a generally opposite direction so that the end thrust on the grinding wheel is in alternately opposite directions. This character of cutting action has the effect on the tool being ground ofvibrating or oscillating the tool, or at least the end region of the tool engaging the wheel at high frequency in alternate transverse directions parallel with the axis of the grinding wheel.

This oscillating or vibrating action of the tool occurs in alternate transverse directions as well as in a direction longitudinally of the tool bit caused by the impacts and intermediate rebounds of the tool away from the Wheel. Successive impacts of the cutting or impinging regions of the wheel engage the tool under the influence of the resilient or yielding pressure which the operator exerts upon the tool holder urging the holder toward the grinding wheel. The recesses 100 and 110 are of substantial depth inthe wheel so that the segments between successive slots or recesses are usable until worn to the depth of the recesses. Thus the periphery of the wheel may be redressed many times before the wheel segments become worn to the bottoms of the recesses.

The grinding wheel or unit may be molded of an ag-.

glomerate of hard abrasive particles held together by a suitable cement 'or bonding agent. The slots in the periphery of the wheel may be of any desired angle depending upon the extent or degree of angular shearing action desired during the grinding operations. As shown in Figure 4, the slots are arranged at substantially an angle of 45 relative to a plane of a side face of the grinding wheel, but it is to be understood that other angular relationships may be established for the slots in order to secure .most effective and etficient grinding operations upon particular materials to be ground.

The leading edges 1.14 of adjacent slots, due to the angularity of the slots, are arranged in converging relation. The widths of the slots in a plane through the wheel normal to the axis of rotation are greater than the vertical dimension of the tool as viewed in Figure 2 so that during grinding operations, the object or tool moves into each slot as the wheel is rotated to bring the slots into successive registration with the tool carried by the tool holder 67.

The degree or extent of movement of the tool or object being ground into the recesses in the grinding wheel is determined by engagement of the template 74 with the straight edge 94, the template having been preset as hereinbefore mentioned so as to permit the removal of a reasonable restricted amount of metal from the object or tool at any one grinding cycle.

When the amount of metal permitted by the predetermined positioning of the template 74 is removed from the tool, a resetting of the tool is required if additional metal is to be removed therefrom. To accomplish this resetting the tool holder is placed upon the ball support 80, the template engaged with the micrometer stop 85 and the position of the tool bit 72 modified as herein fore described.

The method of grinding an .object or tool with the grinding medium or wheel formed with diagonally arranged or oblique slots wherein successive slots extend in generally opposite or diverging directions, the leading edges of the slots successively engage the object or tool in a progressive shearing or slicing action so that at any given instant only substantially point contact or engagement obtains between a cutting edge of the wheel and the tool or work being ground.

Due to the relative high linear speed of the periphery of the grinding wheel, the leading edges of the wheel segments impinge upon the work with substantial irnpact and, due to the minimum area of contact through the progressive shearing action, friction is reduced to a minimum, avoiding burning of the tool and glazing of the wheel with a maximum efficiency in removing metal from'the work or tool. I

The efil'ciency of the cutting or grinding action is augmented or increased through the successive engagement of grinding edge zones extending in successive alternate directions. The successive entry of the work or tool into the slots sets up a. compound vibration or oscillation of the worker tool operative in two directions. With particular reference to Figure 4 as an example, engagement of the leading edge 114 of the adjacent .wheel segment, on impact with a tool entering the slot or reces 110 in the plane of rotation of the wheel, causes the tool to move a slight distance in a right-hand direction, as viewed in Figure 4, under the shearing action of the edge 114 engaging the tool.

At the same time, the impact of a grinding zone or edge 114 with the tool tends to push the tool away from the wheel in opposition to theyielding pressure exerted by the operator upon the tool holder 67 in a direction toward the wheel. After the wheel has rotated to bring the next succeeding slot 100, arranged in a divergent relation to the slot 110, into registration with the tool, the tool enters the slot and is immediately impinged by the leading or cutting edge exerting a shearing action in a generally opposite direction to that caused by the cutting edge 114 of the preceding slot.

The shearing action of the edge 105 is therefore in a generally opposite direction to'that of the edge 1'14, causing the work or tool to be moved slightly in a left-hand direction as viewed in Figure 4, and at the same time, the impact of the edge 105 with the work or tool tends to again push the work away from the wheel in a direction of the plane of rotation of the wheel.

Hence it will be seen that the engagement of successive leading edges 114 and 105 with the tool causes infinitely small movements of the tool, viz. the edge 114 moves the tool slightly in a right-hand direction'and concomitantly moves the tool slightly forwardly away from the Wheel, and the tool, upon registry with the next succeeding slot, is moved in a left-hand direction by reason of the shearing action of the edge 105 and concomitantly therewith the impact urges the tool out of the recess and away from the wheel in the plane of rotation of the wheel. It should be noted that these vibrations or oscillations imparted to the tool are opposed or resisted by the yielding pressure exerted by the operator upon the tool holder 67.

The oscillations or vibrations in a plane normal to the axis of rotation of the wheel and in lateral directions greatly assist or augment the cutting or grinding efiiciency by reason of the striking, impacting or impinging of the leading or cutting edges of the peripheral grinding zones with the tool wherebythe speed of removing metal from the tool or other work is greatly increased over prior methods.

Figures 6 and 7 illustrate a modified form of grinding medium or wheel construction adaptable for carrying out the method of the invention. In this form of wheel construction, the alternate slots 122, diagonally or obliquely arranged relative to a plane through the central region of the wheel and normal to the axis of rotation, are defined by radially converging walls 123 and 124 which lie in planes passing through the central axis or axis of rotation of the wheel as indicated in Figure 6. The leading or cutting edge 125 formed at the junction of the slot wall 124 and the peripheral surface of a grinding wheel segment or zone 126 engaging a tool exerts a shearing action from right to left upon the tool as viewed in Figure 7.

The next succeeding slot is diagonally orobliquely arranged in a generally oppositedirection to that of the slot 122, the pairs of slots being generally arranged in a converging direction or relation as illustrated in Figure'fi. The walls 131 and 132 defining the slot are disposed in radially converging relation as indicated in Figure 6 and lie in planes which at one point pass through the axis of the grinding wheel although the planes are not parallel to the axis of the wheel. The form of wheel shown in Figures 6 and 7 is adapted to carry out the method in substantially the same manner as the wheel configuration shown in Figures 1 through 5.

It is apparent that, within the scope of the invention, modifications and difierent arrangements may be made other than is herein disclosed, and the present disclosure is illustrative merely, the invention comprehending all variations thereof.

I claim:

1. A grinding medium formed with spaced grinding zones defined by recesses, and the leading edges defined by the junctures of Walls of the recesses with surfaces of the grinding zones being diagonally arranged with successive leading edges extending in generally opposite directions, the leading edges of each of the recesses extending the full width of the grinding medium.

2. The method of grinding a tool which includes advancing the tool by yielding pressure against a rotating grinding wheel having grinding zones spaced apart circumferentially a distance greater than the dimension of the tool in the direction of rotation of the wheel and having successive leading edges disposed in alternate angular directions to cause the tool to engage the leading edges of the grinding zones and enter the spaces between the grinding zones in response to the yielding pressure whereby the leading edges by successive impacts with the tool vibrate the tool in directions radially of the wheel and in successive opposed directions transversely of the radial direction of vibration to remove metal from the tool by such impacts, and regulating the amount of metal removed from the tool by positively limiting the extent to which the tool is advanced in a direction radially of the wheel under the influence of the yielding pressure.

3. A grinding wheel of a diameter substantially greater than its width formed with circumferentially spaced grinding zones defined by recesses, and the leading edges defined by the junctures of walls of the recesses with surfaces of the grinding zones being diagonally arranged with successive leading edges extending full width of the wheel and in generally opposite directions, the walls defining each recess being disposed in substantially parallel planes.

4. A grinding wheel of a diameter substantially greater than its width formed with circumferentially spaced grinding zones defined by recesses, and the leading edges defined by the junctures of Walls of the recesses with surfaces of the grinding zones being diagonally arranged with successive leading edges extending full width of the wheel and in generally opposite directions, the Walls defining each recess lying in convergently arranged planes converging in directions toward the axis of the grinding Wheel.

References Cited in the file of this patent UNITED STATES PATENTS 278,608 Schrebler May 29, 1883 888,129 Tone May 19, 1908 909,913 Landis Jan. 19. 1909 964,000 Deelen July 12, 1910 1,029,406 Staynes June 11, 1912 1,582,608 Hyde Apr. 27, 1926 2,049,874 Sherk Aug. 4, 1936 2,195,050 Wallace Mar. 26, 1940 2,607,173 Garrison Aug. 19, 1952 FOREIGN PATENTS 523,879 Great Britain July 24, 1940 

